Conventionally, there is known a structure of a solid oxide fuel cell having “an electrically insulating porous support substrate and having gas flow channels formed therein,” “a plurality of power-generating elements provided on the surface of the support substrate at a plurality of positions, respectively, located apart from one another, each of the power-generating elements being a laminate of a fuel electrode, a solid electrolyte, and an air electrode,” and “a single or a plurality of electrical connections having electron conductivity, provided between a pair of or pairs of adjacent power-generating elements, and adapted to electrically connect the inner electrode of one of the adjacent power-generating elements and the outer electrode of the other one of the adjacent power-generating elements” (refer to, for example, Japanese Patent Application Laid-Open (kokai) Nos. H08-106916 and 2008-226789). Such a configuration is also called “a segmented-in-series type.”
The following description focuses on the shape of the support substrate. In the structure of a “segmented-in-series type” solid oxide fuel cell described in Japanese Patent Application Laid-Open (kokai) No. H08-106916, the support substrate assumes a cylindrical shape. On the surface (cylindrical surface) of the cylindrical support substrate, a plurality of “annular grooves” are formed at a plurality of axial positions for allowing fuel electrodes to be embedded therein, respectively (refer to FIG. 3). Thus, the outside diameter is reduced at the portions of the support substrate where the “annular grooves” are formed. Because of this, this structure can be said to be easily deformable when an external force is applied to the support substrate in a bending direction or a torsional direction.
Also, in the structure of a “segmented-in-series type” solid oxide fuel cell described in Japanese Patent Application Laid-Open (kokai) No. 2008-226789, the support substrate assumes the flat plate having a longitudinal direction. The flat-plate-like support substrate has, on each of its main surfaces (planes), “an elongated groove extending in the longitudinal direction and opening in the longitudinal direction” for allowing fuel electrodes, etc., to be embedded therein (refer to FIG. 3(b)). Thus, the thickness is reduced at the portion of the support substrate where the “elongated groove” is formed.
Additionally, the “elongated groove” has side walls extending in the longitudinal direction at its opposite ends with respect to the width direction orthogonal to the longitudinal direction, but does not have side walls extending in the width direction at its opposite ends with respect to the longitudinal direction. That is, the “elongated groove” does not have a circumferentially closed side wall. Thus, the support substrate does not have a frame which surrounds the “elongated groove.” Because of this, this structure can be said to be easily deformable when an external force is applied to the support substrate in a torsional direction. Thus, the structure of a “segmented-in-series type” fuel cell is desired to provide restraint of deformation of the support substrate when the support substrate is subjected to an external force.
Furthermore, in the above-described fuel cell structure, increasing the power output of each fuel cell is important. One conceivable method of increasing the power output is increasing the electron conductivity between each inner electrode and a corresponding electrical connection.